Typical ion lasers include a laser gas tube enclosing a cathode and an anode, and a laser tube cathode heater for heating the cathode. For example, FIG. 1 shows conventional laser gas tube 2, whose cathode is heated by laser tube cathode heater 14. Cathode heater 14 of FIG. 1 comprises a transformer whose primary winding 17 is connected to an AC power source, and whose secondary winding 18 supplies a lower AC voltage (typically 2.5 VAC, at 25 amps) to the cathode of tube 2. DC voltage can be applied to secondary winding 18 through DC connection line 15.
Cathode heater 14 shown in FIG. 1 is a conventional cathode heater, except that includes an additional sensing winding 16 (to be discussed below) for generating a signal proportional to the voltage induced on winding 18 by primary winding 17.
Thermionic cathodes such as those used in ion lasers should be operated at a temperature specified by the manufacturer for proper operation and long service life. Typically, a cathode is tested in an evacuated bell jar using an optical pyrometer, to adjust the temperature to an optimal value. The optimal heater voltage and current associated with the optimal temperature are measured. In operation, the heater voltage and current applied the cathode are adjusted to their optimal values, typically by selecting taps on a suitable transformer.
This adjustment is limited to coarse steps, and unless a ferroresonant filament transformer is used, the taps should be adjusted in the field (at the user's site) in accordance with the user's line voltage.
The present invention generates substantially constant average (nonfluctuating) AC power for a laser tube cathode heater, in a manner so that the AC power is continuously adjustable (rather than adjustable merely in coarse steps). The invention eliminates the effect of line voltage variation in the field.